JLG 740A, Service And Maintenance Manual

Page: 197 / 408

SECTION 3 - CHASSIS & TURNTABLE
3121160 – JLG Lift – 3-145
Intermittent Malfunction Indicator
Lamp (MIL) The following components can cause intermittent MIL and no DTC(s):
A defective relay, Control Module driven solenoid, or a switch that can cause electrical system interference. Normally,
the problem will occur when the faulty component is operating.
The improper installation of electrical devices, such as lights, 2-way radios, electric motors, etc.
The ignition secondary voltage shorted to a ground.
The Malfunction Indicator Lamp (MIL) circuit or the Diagnostic Test Terminal intermittently shorted to ground.
The Control Module grounds.
Loss of DTC Memory To check for the loss of the DTC Memory:
1. Disconnect the TMAP sensor.
2. Idle the engine until the Malfunction Indicator Lamp illuminates.
The ECM should store a TMAP DTC. The TMAP DTC should remain in the memory when the ignition is turned OFF. If the
TMAP DTC does not store and remain, the ECM is faulty
Additional Checks
No Start
DEFINITION: The engine cranks OK but does not start.
Preliminary Checks Refer to Important Preliminary Checks.
Control Module Checks If a scan tool is available:
Check for proper communication with both the ECM
Check the fuse in the ECM battery power circuit. Refer to Engine Controls Schematics.
Check battery power, ignition power and ground circuits to the ECM. Refer to Engine Control Schematics. Verify volt-
age and/or continuity for each circuit.
Sensor Checks Check the TMAP sensor.
Check the Magnetic pickup sensor (RPM).
Fuel System Checks Important: A closed LPG manual fuel shut off valve will create a no start condition.
Check for air intake system leakage between the mixer and the throttle body.
Verify proper operation of the low pressure lock-off solenoids.
Check the fuel system pressures. Refer to the LPG Fuel System Diagnosis.
Check for proper mixer air valve operation.
Ignition System Checks Note: LPG being a gaseous fuel requires higher secondary ignition system voltages for the equivalent gasoline operating
conditions.
Check for the proper ignition voltage output with J 26792 or the equivalent.
Verify that the spark plugs are correct for use with LPG (R42LTS)
Check the spark plugs for the following conditions:
- Wet plugs
- Cracks
- Wear
- Improper gap
- Burned electrodes
- Heavy deposits
Check for bare or shorted ignition wires.
Check for loose ignition coil connections at the coil.
Engine Mechanical Checks Important: The LPG Fuel system works on a fumigation principle of fuel introduction and is more sensitive to intake man-
ifold leakage than the gasoline fuel supply system.
Check for the following:
- Vacuum leaks
- Improper valve timing
- Low compression
- Bent pushrods
- Worn rocker arms
- Broken or weak valve springs
- Worn camshaft lobes.
Table 3-13. Symptom Diagnosis
Checks Action